1. Field of the Invention
The present invention relates to a method for manufacturing a fluorescent lamp having an interconnected portion in the glass tubes.
2. Description of the Related Art
In the prior art, a fluorescent lamp with a prolonged discharge path, which is achieved by interconnecting glass tubes, is known in the form of a bulb fluorescent lamp, a compact fluorescent lamp, and so forth. One means for interconnecting glass tubes as described above is, for example, as shown in JP63(1988)-107830A, to heat and melt interconnecting portions of parallel arranged glass tubes respectively from inside the glass tubes by burners, to interconnect the glass tubes through a communicating aperture formed by the wind pressure of the burners, to pinch and close the tube end portions, and then to reheat the tube end portions and put them into a predetermined mold for forming the tube ends into a predetermined shape. In addition, another way of forming a communicating aperture by the above-mentioned interconnecting means has been tried, in which the inner walls of the heated glass tubes are thinned by lightly tapping them once or twice with small metal plates from inside the glass tubes, and then, the thinned parts of the glass tubes are blown open by the wind pressure of the burners to form apertures.
However, in the case of using the conventional means for forming an interconnected portion in glass tubes mentioned above, when the aperture is formed only by the wind pressure of a burner, due to the sharpness of the flames from the burner nozzle, the aperture has a small diameter, and thus the discharge path of the glass tubes partially has a smaller diameter, so that the luminous characteristics of the fluorescent lamp may become unstable. Furthermore, in the case of thinning the glass tube in advance and opening the glass tube by the wind pressure of the burner, since the glass thickness in the interconnected portion varies due to a change in the direction and the wind pressure of the burner flames, extremely thin portions and extremely thick portions are created in the upper, lower or lateral parts of the interconnected portion, thereby causing distortion. As a result, there was a problem of causing a crack failure in the interconnected portion during the manufacturing process of the fluorescent lamp or while lighting the completed fluorescent lamp.
The present invention solves the conventional problems described above in such a manner that the aperture of the interconnected portion of the glass tubes is formed with a diameter that does not interfere with the performance of the fluorescent lamp and also that breakage of the interconnected portion is prevented during each manufacturing process or after the fluorescent lamp is completed.
In order to solve the problems described above, it is an object of the present invention to provide a method for manufacturing a fluorescent lamp, comprising heating interconnecting portions located in the vicinity of open end portions of glass tubes that are positioned adjacent to each other respectively from inside to form a welding portion, thrusting the glass tubes against each other and thinning them by conducting a preliminary tapping of the welding portion from inside using hammers, opening the welding portion by conducting a main tapping using hammers to form an interconnected portion, closing end portions in the vicinity of the interconnected portion by heating and melting, and molding the end portions.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a thickness of the glass tube is in a range of 0.75 mm to 1.50 mm.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a heating temperature for the interconnecting portions is in a range of 900xc2x0 C. to 1400xc2x0 C.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that the hammer has an elliptical tip with a minor axis of 3 mm to 7 mm and a major axis of 4 mm to 12 mm.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a pressure of the preliminary tapping is in a range of 1.1 MPa to 2.2 MPa.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, a pressure of the preliminary tapping and a pressure of thrusting the glass tubes against each other may be approximately the same.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a pressure of the main tapping is in a range of 1.1 MPa to 2.2 MPa, more preferably 1.8 MPa to 2.2 MPa.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, a pressure of the main tapping may be larger than a pressure of the preliminary tapping.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that an aperture of the interconnected portion has an elliptical shape with a minor axis of 3 mm to 10 mm and a major axis of 4 mm to 15 mm, more preferably with a minor axis of 3 mm to 7 mm and a major axis of 4 mm to 12 mm.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a heating temperature in the vicinity of the interconnected portion is in a range of 900xc2x0 C. to 1400xc2x0 C.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that the molding is conducted at a temperature of 930xc2x0 C. to 1200xc2x0 C., more preferably 930xc2x0 C. to 1030xc2x0 C.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a space between the glass tubes is not less than the thickness of the glass tube.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that the preliminary tapping is conducted once or twice, and the main tapping is conducted for two or more times by the hammers.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that the glass tubes are at least partially uncoated by phosphor before the interconnected portion is formed.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, cooling zones can be provided in portions where the glass tubes are molded.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, the glass tubes may be linear or nonlinear glass tubes.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a phosphor coating is formed partially or entirely on an inner surface of the glass tube after the process of forming the interconnected portion or molding.
Furthermore, in the method for manufacturing a fluorescent lamp of the present invention, it is preferable that a thickness of the phosphor coating is in a range of 20 xcexcm to 30 xcexcm.
According to the method for manufacturing a fluorescent lamp of the present invention, the interconnected portion of the glass tubes can be formed by the steps of heating the interconnecting portions of glass tubes respectively from inside and softening them approximately to the melting point, lightly contacting the glass tubes against each other and thrusting and thinning them by conducting the preliminary tapping once or twice by the hammers, conducting the main tapping repeatedly for two or more times, and forming the apertures with a large diameter by partially ripping off the glass walls so as to avoid the glass walls having an uneven thickness. Therefore, a distortion occurring in the interconnected portion can be prevented. Moreover, with respect to the opening end portions of the glass tubes near the interconnected portion, as the process following the interconnection of the glass tubes, the open end portions are heated, melted and closed locally after the interconnection is completed, and then, the glass tubes are molded in the softened state to shape the end portions by using a mold of a predetermined shape. Thus, the steps from the formation of the interconnected portion to the molding of the end portions of the glass tubes can be conducted continuously, so that the production efficiency can be improved. In particular, since there is no coating such as a phosphor coating or a conductive film formed on the inner walls of the glass tubes in the interconnecting portions or in the portions where the end portions of the glass tubes are formed, the conditions for the interconnecting process and the molding process also are simple, and the problems such as unevenness and variance in the thickness, unevenness in the shape, and reduction of the glass strength can be solved.